Power plants smelters steel mills, cement plants and paper and pulp plant operations are attended by large volumes of exhaust gases which are variously processed before being discharged.
By way of but two examples of exhaust gas processing, an exhaust gas system may be provided with parallel branches containing environmental pollution abatement equipment such as bag houses, electrostatic precipitators or scrubbers with each branch equipped with dampers enabling it to be isolated and entered when service therein is required As another example, the exhaust system of a gas turbine, kiln, furnace or other incineration process may be provided with a diverter equipped with a damper operable to direct the hot gas through a heat recovery steam boiler or to divert such gas to a bypass system.
The ducts which are to include such dampers vary greatly in size but are typically large with some twenty feet by twenty feet by way of one example. The larger the cross sectional dimensions of a duct, the more difficult it is to provide a seat for a seal which is capable both of effective sealing engagement therewith and of withstanding the rigors of use.
In one type of damper, blades slide across the ports and are marginally sealed in various ways. One such way employs a seal having a pair of cantilever leaf spring sets with the leaf springs of each set successively decreasing in width and with both sets disposed to be flexed as the blade passes between them with the widest leaf springs then seated against the margins of the blade. In one such arrangement, see U.S. Pat. No. 4,088,146, the cantilever leaf spring sets were not flexed until the blade forced them apart while in U.S. Pat. No. 3,504,885, the seals between which the blade passes are held flexed by each other until forced apart by the blade and each is backed by a leaf spring.
Leaf springs, due to their flexibility and resilience are also well adapted for use in dampers having blades which are centrally pivoted, which are connected at one end to a pivot shaft or which are otherwise supported for movement lengthwise of the flow path through a port.
One type of cantilever leaf spring seal for such uses utilizes a bias leaf spring in conjunction therewith. In U.S. Pat. No. 3,698,429, the bias leaf spring holds the cantilever leaf spring tensioned at all times while in U.S. Pat. No. 4,325,411 the cantilever leaf spring is not affected by the bias leaf spring until the port is closed, both springs then becoming tensioned.